Hi all, I have a 1980's Sugino crank and it has 684 and 171 stamped on it.The front chain wheels are a 52 and I think 48 or 49.I think it's a Sugino Mighty but unsure.I would like to change the small chain ring to a lower ratio then it's current high ratio of 48 or 49 to something around a 40 or 39.I can't seem to find a wheel to buy, am I able to change the wheel?

Should be able to, unless it's an especially cheap Sugino with riveted/pressed rings.

Read up about BCDs and how to measure your crank and know which size chain ring to buy here

Seems a little odd that your existing chain rings are so close together in size - normally there's at least a 10 tooth difference. eg 52/42, 53/39 etc... etc. though this can depend on the age of the bike and the original ratio combinations with the rear cassette/cluster though.

It's not really the best photo for guaging by eye what you have. Odds are it's a 130mm.. or possibly if it's an older 70s road double maybe 144bcd. If the latter is the case.. you'll probably be limited to track chainrings in this day & age, which are meant for 1/8" chains - not multi-speed 3/32" geared set ups.

144 as a road (geared) BCD died out back when rear clusters were no more than 5 (or 6?) cogs at the back... but there are still a number of these 144 doubles (i.e. two chain ring) around.

There's a limit to how small they can get depending on your BCD. I think the smallest 144bcds you can get are about 42/43 tooth ? (don't quote me) but it's a geometry limitation traded off with rigidity & strength.... so I'd wonder if you could ever get much lower than 48/49 on a 151 bcd.... let alone if can get one in this day & age.

The smaller the BCD, the lower the minimum tooth count. Physically there's no limit to the max tooth count (not taking into account frame clearances against the chainstays etc) but you lose rigidity as the crank spider gets smaller in relation to the larger chainring.

I'd be dubious about buying an old second hand ring for any sum of money.... if you're heart is set on using your cranks, Cooker.... contact these guys, who do custom jobbies; www.cycleunderground.com.au or even Fyxomatosis (whom Cycleunderground apparently makes 'rings for)

Don't give up on your old 151 BCD Sugino's. Plenty of 3/32 151 rings come up on eBay. A small amount of wear is not a huge issue as these older rings are not ramped or pinned and generally have larger teeth meaning chain slip is not a big concern.

Problem is, I need an inner ring.My crank has 2 rings, 48/53.I want an inner ring less then 48 and all the 151 rings I have found are for single speed that doesn't recquire changing gear.Are yours inners?

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